After three years and 125+ trips I'm refinishing my SW17. I have a number of scratches on the bottom I would like to fill in with epoxy. How do I know if I have all the varnish off the bottom before rolling new coat of epoxy? Will epoxy stick after I sand if there is any varnish left? I sanded the whole boat with 240 wet/dry so not worried about top deck and varnish only.